Laser Communication Network Research Articles

Research progress of space laser communication networking technology

Research progress of space laser communication networking technology

Research on Quadrant Detector Multi-Spot Position Detection Based on Orthogonal Frequency Division Multiplexing

Free space optical communication is developing towards laser communication networking. A novel method of quadrant detector (QD) multi-spot position detection based on orthogonal frequency division multiplexing (OFDM) is proposed for multi-spot laser communication systems. The mathematical model is constructed, and the Monte Carlo method is used to validate it. The position calculation of three beams incident on QD is simulated. The influence of key parameters on the accuracy of position detection is analyzed when the spots are at the same position and a different position. The results show that when the SNR of the system is 31.74 dB, the radius of the Gauss spot is 2 mm, the number of FFT (fast Fourier transform) points is 1024, and the center of the multi-spot is at the same position of the detector target; the accuracy of signal position detection calculated by the equation is 1.433 μm, and the simulation results are 1.351 μm, 1.354 μm, and 1.389 μm, respectively. When the center position of the multi-spot is at different positions of the detector target, the detection accuracy calculated by the formula is 1.438 μm, 1.433 μm, and 1.434 μm, respectively, and the simulation results are 1.419 μm, 1.387 μm, and 1.346 μm, respectively. The experimental results verify the effectiveness of the proposed multi-target simultaneous detection method. This article proposes a new multi-spot position detection method which can not only achieve one-to-multiple node laser communication but also improve the accuracy of point position detection.

Research on laser target dynamic tracking system with rotating polarization grating.

A micromechanical target tracking system based on polarization grating (PG) is designed to meet the conformal design of laser communication systems and to realize the lightweight and miniaturization of space laser communication networking. The rotating dual PGs are applied to the dynamic tracking of laser targets for the first time, the relationship between the target position and the dual polarization gratings (PGs) angles is defined, and the PG beam deflection multi-coordinate construction and decoupling are carried out. A dual PGs mathematical model was established, and a controller based on the dual PGs system loop was designed. After calibration and dynamic verification of the dual PGs, the unmanned aerial vehicle (UAV) tracking experiment is conducted for the first time, and the dual axis closed-loop tracking error of the dynamic target is within 300µrad (RMSE). The feasibility of dual PGs tracking formula, the feasibility of laser target fixed-point closed-loop control, and the dynamic closed-loop tracking performance are verified. In engineering applications, the dual PGs tracking system has guiding significance for realizing the lightweight and miniaturization of system integration, as well as the possibility to replace the traditional tracking control system.

Numerical Calculation for the Line-of-Sight Attitudes of Multi-Address Transceivers without 2:1 Transmissions for Space Laser Communication Networking

In order to optimize space laser communication networking, the 2:1 transmissions for all reflectors on a multi-address transceiver can be removed. However, without the 2:1 transmissions, the reflectors exhibit doubled optical coupling effect in rotation, which reduces the numerical calculation precision of the attitudes of the reflectors’ lines-of-sight (LOS). In the present study, using Snell’s law of reflection and Euler’s theorem, a mathematical model for the attitudes of the LOS of multiple reflectors without 2:1 transmissions was established, and a method was proposed for an indirect numerical calculation of the attitudes of the LOS by creating a Snell transformation matrix. This method eliminates the influence of the doubled optical coupling effect on the numerical solution of the line-of-sight attitudes of multi-reflectors. Compared to the direct numerical calculation method using the angular velocity, the calculation precisions achieved using the proposed method exhibited improvements of 3, 5, and 3 orders of magnitude in the three conical motions, respectively. The indirect calculation method and the numerical calculation model proposed in the present study, therefore, provide a theoretical basis for applying reflectors without 2:1 transmissions to multi-address transceivers.

A study of modeling method of strapdown stable attitude in laser communication networking

A study of modeling method of strapdown stable attitude in laser communication networking

Prototype development of multi-target tracking system for space multi-node laser communication network

Laser communication network is the future trend, but the disadvantage of a traditional laser communication system is that it can only transmit with a single node. To solve this problem, we propose a multi-target tracking technology to simultaneously establish multiple laser communication links. This study also develops a multi-target detection method based on beacon modulation and code division multiple access, proposes an optical antenna central stabilization method, and enhances the controller of the fast steering mirror (FSM) to improve the tracking performance. To verify the feasibility of our proposed method, we build a prototype system for multi-target laser communication and conduct the corresponding experiment. The experiment simulates the multi-target tracking situation by three beam emitting subsystems, and the dynamic tracking performance of the prototype system is verified by applying perturbations through a shaking table. Results show that the proposed method can effectively extract the position of the target in the mixed beam, with an average detection deviation of 2.95 μrad compared with when only a single beam is incident. The introduction of central stabilization enhances the dynamic tracking performance of the optical antenna. Tracking accuracy of the optical antenna is 24.63 μrad when attitude disturbance is applied. The improved controller enhances the performance of FSM, composite tracking accuracy is 5.69 μrad, and tracking error is reduced by 22.16% compared with the traditional PI controller. Performance also improved by 45.42% compared with when there was no improvement. Experimental results verify the effectiveness of the multi-target tracking system. On the basis of the proposed method, we achieve simultaneous tracking of multiple targets in different directions and significantly improve the dynamic tracking performance.

Dynamic Network Formation for FSO Satellite Communication

Satellite network optimization is essential, particularly since the cost of manufacturing, launching and maintaining each satellite is significant. Moreover, classical communication optimization methods, such as Minimal Spanning Tree, cannot be applied directly in dynamic scenarios where the satellite constellation is constantly changing. Motivated by the rapid growth of the Star-Link constellation that, as of Q4 2021, consists of over 1600 operational LEO satellites with thousands more expected in the coming years, this paper focuses on the problem of constructing an optimal inter-satellite (laser) communication network. More formally, given a large set of LEO satellites, each equipped with a fixed number of laser links, we direct each laser module on each satellite such that the underlying laser network will be optimal with respect to a given objective function and communication demand. In this work, we present a novel heuristic to create an optimal dynamic optical network communication using an Ant Colony algorithm. This method takes into account both the time it takes to establish an optical link (acquisition time) and the bounded number of communication links, as each satellite has a fixed amount of optical communication modules installed. Based on a large number of simulations, we conclude that, although the underlying problem of bounded-degree-spanning-tree is NP-hard (even for static cases), the suggested ant-colony heuristic is able to compute cost-efficient solutions in semi-real-time.

Inter-satellite laser-ranging based on intradyne coherent detection

With the development of laser communication networking, laser-ranging technology is becoming more and more applicable. In this paper, high-accuracy ranging is implemented based on intradyne coherent detection at a communication rate of 1048.576 Mbps. The ranging accuracy is affected by clock phase calculation error and code loop track error. Parallel clock phase difference calculation, frame head correlation, and ranging ambiguity region handle are combined with the ranging calibration method, realizing millimeter-level corrected distance measurement. Dynamic range measurement above 1 m is proven to be continuous through the ranging ambiguity region handle. In addition, high-precision clock frequency deviation between two asynchronous terminals can be obtained through derivation of one-way distance at static ranging or by derivative of distance difference at bidirectional ranging. The methods proposed in this paper are verified by inter-satellite laser-ranging on orbit, and the results are analyzed.

Mode analysis of atmospheric turbulence mitigation with Multi-Plane Light Conversion

Developing standard and accessible atmospheric turbulence mitigation is of paramount importance to enable laser communication network deployment. Multi-Plane Light Conversion (MPLC) [1]–[3] is proving to be an effective technique to improve coupling efficiency of a perturbated wave-front profile towards a single-mode fiber [4]–[6]. However, to date, experimental studies are restricted to a fixed number of modes. In this work, we numerically and experimentally study performance improvement of the MPLC technique and mode collection compared to direct single mode fiber coupling for several D/r0 ratio, D being the receiver aperture diameter and r0 the Fried parameter. We calculate the coupling efficiency, represented in Fig 1. Collection for SMF only is shown in Fig 1-a while the summation of the 15 first Hermite-Gaussian modes is represented in Fig 1-b. Collection for each mode for D/r0=4 is displayed in Fig 1-c. We demonstrate that 15 modes MPLC appears to be a good compromise between number of modes and complexity of the device. This configuration typically improves the collection efficiency by >7 dB in the case of strong turbulence when D/r0 >4. More important, the minimum collection efficiency that would correspond to a link failure is dramatically increased compared to SMF fiber alone. MPLC thus shows high robustness to turbulence fluctuation.

Tracking Performance of Mirrors in Space Laser Communication Networking

Tracking Performance of Mirrors in Space Laser Communication Networking

Control Technology of Slave Optical Transceiver in Space Laser Communication Network

Control Technology of Slave Optical Transceiver in Space Laser Communication Network

Construction and maintenance of satellite-to-ground and inter-satellite laser communication network

Construction and maintenance of satellite-to-ground and inter-satellite laser communication network

Networking optical antenna of space laser communication

Laser communication network technology has not been broken through and it needs to meet the demands of “high-speed, real-time, dynamic and big range” among platforms, which seriously restricts large-scale engineering application and space network system. To solve the problem of communication platform for networking, a new solution based on rotating parabolic model and a new scheme of laser communication networking antenna system has been put forward in the paper. Depending on the operation mode of the system, multiple mathematical optimization models have been established. Tracking communication range, emission energy efficiency, and receiving energy efficiency have been analyzed and optimized. Relationship among opening up and low apertures, lens unit aperture, focal length of lens unit as well as rotating parabolic focal length have been analyzed. After preliminary optimized design of the system, demand of three satellites in 1000 km, 360° circumferential range, pitch range greater than 20° under the condition of network communication can be reached. Under the background of three LEO (low earth orbit) satellites within 1000 km distance of 2.5 Gbps rate in networking, communication link energy is analyzed and calculated to meet the smallest and the lightest of laser emission energy. Relationship between track angle and receiving as well as emission energy is analyzed. Conclusions can promote various fields of engineering, large-scale applications, and updated generations.

AD 4D Hyperlocal Would Like to Use Your Current Location

The physical nature of current location‐tracked mobile culture can open up new sites to explore our relationship to place and question our cultural reliance upon it. Recent projects by London‐based multidisciplinary design studio UniversalAssemblyUnit playfully offer a shared‐ownership alternative to commercially driven centralised networks. The studio's cofounders Will Gowland and Samantha Lee here outline three such projects, involving a weather visualiser for Alaska, a laser communication network for Mexico City and a virtual replica of woodland for East Sussex.

Optical multiaccess free-space laser communication system

With urgent demand for an integrated information network and development of free-space laser communication technology, research on high-rate laser communication networking technology is vital. This study analyzed the technical difficulties related to space laser communication networking and proposed a laser communication networking solution. A wide-angle beam expander and dual-rotating prism group were incorporated into a multiaccess optical laser communication antenna. The wide-angle beam expander collects signal light from different directions; the dual-rotating prism group tracks different targets simultaneously. This paper presents an overall scheme allowing multiaccess free-space laser communications based on the optical antenna described and the associated relay optics and transceiver subsystems.

空间激光通信组网中旋转抛物面基底面型研究

空间激光通信组网中旋转抛物面基底面型研究

광역 화재감지를 위한 적외선 레이저 연기 검출 시스템의 설계 및 구현

In this paper, we propose a smoke detection system in order to detect a fire in a wide space, such as tunnel, airports using infra-red and visible laser. The proposed smoke detection system is composed of infra-red laser transmitter and receiver, visible laser and Zigbee wireless communication network. A visible laser is used to match transmitter and receiver and Zigbee network is utilized to propagate warnings of fire. If smoke is appeared between transmitter and receiver, received signals are decreased and it can be considered as occurring smoke. As IR laser transmitter and receiver are separated by long distance, it is difficult to match due to large variations caused by small change of direction. In this paper, it is proposed to match effectively using visible laser. When smoke is detected, warning informations are propagated by Zigbee network in the developed smoke detection system.